The present invention relates to a fluid pressure control device for a vehicle braking system, and more particularly to a fluid pressure control valve unit of the type in which an inertia-controlled valve assembly is adapted to control the braking pressure applied to rear wheel brake cylinders from a master cylinder in accordance with the rate of deceleration of the vehicle.
The inertia-controlled valve assembly of this kind includes a movable ball disposed within a valve chamber to co-operate with a valve seat and rolling toward the valve seat on the inclined bottom of the chamber. The valve assembly is usually mounted at an inclined angle on a vehicle body frame supported by a suspension system such that the ball rests under gravity in a normal position to open the valve and rolls toward the valve seat to close the valve when the ball is subjected to a deceleration in excess of a predetermined value. In practical use of the valve assembly, if the master cylinder is rapidly operated by emergent depression of the brake pedal, the emergent braking operation causes forward displacement of the vehicle body frame against the spring suspended wheel axles due to the moment of inertia. This decreases the rate of deceleration acting on the ball less than that acting on the wheel axles and subsequently the rolling operation of the ball delays to occur mis-operation of the fluid pressure control device.